Reevaluation of the well permeameter as a field method for measuring hydraulic conductivity

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Abstract
Improved theory of steady outflow of water ponded to constant depth in holes drilled in unsaturated soil is used to re-evaluate the well permeameter method for measurement of in situ hydraulic conductivity, Kg. In particular, theory predicts that neglect of unsaturated flow into soil surrounding the saturated region around a borehole may lead to serious overestimation of K0, especially when using small holes in soils with high capillarity, i.e. the capillarity factor á = 0.1-1 m-l. Field studies on 12 soils gave a values from 6 to 35 m-l, resulting in theoretical overestimates of K0 by 10-40%, for boreholes >0.3 m deep and >0.03 m radius. Comparison of results obtained by measurements with this method for four soils, however, gave permeameter values of K0 which were approximately 50% of those obtained with the augerhole or the core method. Overestimation of K0 due to neglect of capillarity was, in all cases, more than offset by reduction in K0 due to pore closure around a hole during drilling and infiltration.